There is a long history of efforts to develop and perfect air-operated pumps because they offer the promise of fluid pumping without the use of prime mover elements such as pistons, impellers, diaphragms, or other mechanical components such as are required in other forms of pumps. As a result, the advantage of air-operated pumps should consist not only in a reduction of the number of moving parts, with attendant simplification and greater reliability, but also in an enhanced ability to safely and dependably pump corrosive and noxious fluids. Many earlier pumps were endowed with so great a proliferation of moving parts that their use with non-homogeneous fluid-mixtures would lead to early failure through either increased friction or inevitable corrosion. Thus the ideal of an air-operated pump that would operate under a great variety of difficult circumstances, and would be long-lasting and free of corrosion problems, and would have an absolute minimum of moving parts, has proved elusive.
A predecessor invention, described in U.S. Pat. No. 4,467,831, issued Aug. 28, 1984, to French did accomplish many of the above objectives, particularly in that the liquid-detection mode and the pumping mode were combined in the function of a single moving part, thus achieving great simplicity and reliability in the resultant pumping system. While in the typical centrifugal pump the failure of a separate liquid-level control will doom the pump to run dry until it is either manually turned off or else it burns up, the combination in this new pump of liquid-detection with actual pumping prevented the failure mode that has long plagued electrical and air-operated centrifugal pumps.
Another feature of the predecessor pump was the fact that no energy was used until pumping was triggered and the unit began to operate. This triggering occurred when liquid had risen to that point in the chamber where the control-gate valving means finally lifted up off its valve seat to initiate pumping. In the real world, where the conservation of energy has a high priority, this non-consumption of energy when the pump is in an idle mode is of very great importance. Thus the referenced Aikman pump (U.S. Pat. No. 1,658,031) as well as compressed-air-operated centrifugal pumps, and substantially all the rest of the known prior art, constantly leaked air to a greater or lesser extent during the idle or resting portion of the pump cycle. Indeed, the chronic problem with not just pumps alone, but with fluidic devices in general, and one major reason for their lack of more general use, has been that they more or less constantly bleed off or dissipate power during the non-working or "null" part of their duty cycle.
But the prior invention suffered several serious limitations:
[1] Pumping capacity was low because the rate at which compressed air could be admitted into the pumping chamber was low (due to air-pressure-dependent valve geometry), with the result that the pump was practical only for small installations with limited pumping needs.
[2] An excessively long time was needed to vent used air out of the pumping chamber: before a new charge of liquid could be admitted by gravity, the space in the chamber above the liquid had to return to atmospheric pressure. This venting became slower as the pressure inside the chamber decreased, thus causing the air-exhaust portion of the pumping cycle to be awkwardly long and so in turn seriously limiting the pumping efficiency of any system utilizing this principle.
[3] High pumping heads were not practical (in deep wells, for example): Because of the pump's too-simple design, the pressure needed for the liquid-level detection mode, as well as the ultimately available compressed-air pumping pressure, necessarily both had to be one and the same. This meant that the greater pressures required for pumping against higher heads required tinier orifices through which air was admitted, so that the net downward force holding a valve poppet closed would not otherwise exceed such upward displacement forces as were practically attainable in the limiting geometry of well pumps.